1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

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分析：

利用map记录前面数的情况，为了区别第一个数，给置了标志，其实应该可以更简单。

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> v1;
        map<int,int> m1;
        m1[nums[0]]=-1;
        for(int t=1;t<nums.size();++t)
        {
            if(m1[target-nums[t]]!=0) {
                if(m1[target-nums[t]]==-1)
                v1.push_back(0);
                else
                v1.push_back(m1[target-nums[t]]);
                v1.push_back(t);return v1;}
            else
            {
                m1[nums[t]]=t;
            }
        }
    }
};